Technical Field
The present invention relates to a method for producing a composite of cubic boron nitride (cBN) dispersed in a SiAlON ceramic.
Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
Ceramics serve a traditional role as durable materials that are able to withstand extreme temperatures and pressures. One of the ceramics that exhibits outstanding thermo-mechanical resilience is silicon nitride [Riley, F. L. J. Am. Ceram. Soc 83 (2000) 245-65—incorporated herein by reference in its entirety]. However, the synthesis of fully compact and densified silicon nitride materials is challenging given the strong covalent character of its chemical bonds, which require excessively high temperatures to overcome [Hampshire, S. “The Role of Additives in the Pressureless Sintering of Nitrogen Ceramics for Engine Applications.” Metals Forum. Pergamon Press 7 (1984) 162-70 and Hampshire, S. Materials Science Forum Trans Tech Publications 606 (2009) 27-41—each incorporated herein by reference in its entirety]. However, certain metal oxide additives to silicon nitride, combined with synthesis at high temperatures as well as sufficiently long sintering periods, have led to the development of fully compact materials at much lower temperatures [Riley, F. L. J. Am. Ceram. Soc 83 (2000) 245-65; Hampshire, S. “The Role of Additives in the Pressureless Sintering of Nitrogen Ceramics for Engine Applications.” Metals Forum. Pergamon Press 7 (1984) 162-70; Hampshire, S. Materials Science Forum Trans Tech Publications 606 (2009) 27-41; and Hampshire, S. et al. “Grain Boundary Glasses in Silicon Nitride: A Review of Chemistry, Properties and Crystallisation.” J. Eur. Ceram. Soc 32 (2012) 1925-32—each incorporated herein by reference in its entirety]. An obvious outcome of this additive modification was the development of sialon materials, which have an additive-controlled structure-property relationship [Jack, K. H. et al. Nature 238 (1972) 28-9; Oyama, Y. et al. Jpn. J. Appl. Phys 10 (1971) 1637; and Hampshire, S, et al. Nature 274 (1978) 880-2—each incorporated herein by reference in its entirety].
Although rare-earth metal oxides have been employed as stabilizing additives in the sintering of sialons for decades, calcium oxide lately has become a favorable additive due to its higher solubility and stability [Herrmann, M. et al. J. Eur. Ceram. Soc 32 (2012) 1313-9; Menke, Y. et al., “Effect of Rare-Earth Cations on Properties of Sialon Glasses.” J. Non-Cryst. Solids 276 (2000) 145-50; Bandyopadhyay, S. et al. Ceram. Int. 25 (1999): 207-13; Hakeem, A. S. et al. J. Eur. Ceram. Soc 27 (2007) 4773-81; Wang, P. L. et al. Mater. Lett 38 (1999) 178-85; and Wang, P. L. et al. J. Eur. Ceram. Soc 20 (2000) 1333-7—each incorporated herein by reference in its entirety]. Moreover, the low cost and high availability of Ca-based compounds has been an additional advantage for their use as sintering aids [Van, R. et al. Ceram. Int. 27 (2001) 461-6—incorporated herein by reference in its entirety].
While the use of metal oxide additives has enabled the sintering of silicon nitride ceramics at less extreme temperatures, the advent of spark plasma sintering (SPS) has additionally provided a faster synthesis route than traditional sintering methods such as hot pressing and hot isostatic pressing [Belmonte, M. et al. J. Eur. Ceram. Soc 30 (2010) 2937-46—incorporated herein by reference in its entirety]. SPS is a consolidation technique that has gained attention for the synthesis of ceramic materials due to its higher heating rate, shorter synthesis duration, and novel pulsed-current based heating [Liu, L. et al. J. Eur. Ceram. Soc 30 (2010) 2683-9 and Salamon, D. et al. J. Eur. Ceram. Soc 27 (2007) 2541-7—each incorporated herein by reference in its entirety].
In view of the foregoing, one objective of the present invention is to provide a method for producing a composite of cubic boron nitride (cBN) dispersed in a sialon ceramic. Another objective is to provide a densified, e.g., fully densified, cBN-reinforced sialon composite produced at a sintering temperature of as low as 1500° C., which gives rise to mechanical properties having contradictory natures, i.e. high hardness along with medium to high fracture toughness.